please have a look at the post of @MCG which is a good explanation on what to do if you are new to radar and want to start InSAR analyses.
and also:
ESA provides nice explanations on interferometry: ESA - InSAR Principles: Guidelines for SAR Interferometry Processing and Interpretation<br>(ESA TM-19)
Here you will find three documents:
**Part A** is for readers with a good knowledge of optical and microwave remote sensing, to acquaint them with interferometric SAR image processing and interpretation. **Part B** provides a practical approach and the technical background for beginners with InSAR processing. **Part C** contains a more mathematical approach, for a deeper understanding of the interferometric process. It includes themes such as super resolution and ERS/Envisat interferometry.